Dispersion of fine particles for various applications, such as plasma spray deposition, combustion, and the like, has been successfully accomplished for particles of relatively large size. Once a minimum particle size is reached, such as less than ten microns, particle attraction forces overcome gravitational forces resulting in clumping and cohesion of the particles. When this occurs, dispersion of these very fine particles is difficult to achieve.
A specific area of interest is the use of particles in plasma sprays. Currently, plasma sprays are employed for material deposition, formation and alloying. RF plasma spray devices inject powders formed of fine particles into plasma created by RF induction coils. The particles in the powder can be softened or even completely melted. The particles are then deposited from the plasma onto a substrate or cooled, allowing surface tension to create spheres of the material which are then collected. While very useful for relatively large particles, such as particles greater than 10 microns, smaller Nano sized particles do not work well in RF plasma spray devices. Specifically, as the particle size decreases, such as less than ten microns, inter-particle forces are equal or greater than gravity, resulting in clumping of the powders. Recently, plasma devices have been made which permit very fine particles to be efficiently injected into plasma for deposition. These devices are employed in what is called suspension plasma spray.
Suspension plasma spray devices utilize particles suspended in a liquid carrier. The suspension is brought into the plasma discharge as a stream of fine droplets by an atomizing probe. Very fine particles are easily handled with the suspension. When the suspension is introduced into the plasma discharge, the carrier substance is vaporized with the particles agglomerating into partially or totally melted drops. These drops are then deposited or collected as desired. While effective, the droplets contain multiple particles which agglomerate with vaporization of the carrier. Thus, the resulting agglomerated material includes multiple particles, the agglomeration having a much greater size than the individual particles. Additionally, this method is used as a means of alloying materials. When particles of different materials are employed, the partial or complete melting of the agglomerated materials results in partially or completely alloyed material.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object the present invention to provide a new and improved method of dispersing fine particles in a spray.
Another object of the present invention is to provide a method of dispersing very fine particles in a gaseous spray.
Yet another object of the present invention is to provide a method of simultaneously depositing very fine particles of different materials.